Published · Updated
Medically reviewed by Danesh Alam MD, DFAPA, DFASAM
Stimulants such as cocaine, amphetamines, methamphetamine, and MDMA, and hallucinogens such as LSD and psilocybin, commonly make the pupils larger. So can anticholinergic substances, including antihistamine overdoses and jimsonweed, and some prescription and over-the-counter medicines. Opioids do the opposite: they usually make pupils very small.
Pupil size alone cannot tell you whether someone has used a drug. Pupils also enlarge in dim light, with strong emotion, and after dilating eye drops, and some people naturally have large pupils. A clinician considers lighting, medicines, symptoms, and medical history when assessing a change. MedlinePlus: Anisocoria.
If someone has dilated pupils along with confusion, a very high temperature, a racing heart, a seizure, or trouble breathing, call 911. For poisoning questions, call Poison Help at 1-800-222-1222.
How drugs change pupil size
Two small muscles in the colored part of the eye set the size of the pupil. One ring-shaped muscle tightens the pupil and is controlled by the "rest and digest" (parasympathetic) nerves. Another pulls the pupil open and is driven by the "fight or flight" (sympathetic) nerves. StatPearls: Pupillary light reflex.
A drug can enlarge the pupils in two main ways: by boosting the signal that opens them, as stimulants do, or by blocking the signal that closes them, as anticholinergic drugs do. Opioids make pupils small by strengthening the closing signal.
Drugs and medicines that can dilate pupils
Stimulants. Cocaine, amphetamine, methamphetamine, and MDMA (ecstasy) increase norepinephrine activity, which opens the pupils. NIDA lists dilated pupils among cocaine's short-term effects, along with a faster heart rate and higher blood pressure and body temperature. NIDA: Short-term effects of cocaine. Synthetic cathinones, sometimes sold as "bath salts," have similar effects and can be life-threatening. NIDA: Synthetic cathinones.
Hallucinogens. Psychedelics such as LSD and psilocybin act mainly on serotonin receptors in the brain. Poison center data cited by NIDA list pupil dilation among their most common short-term physical effects, along with agitation and a rapid heartbeat. NIDA: Psychedelic and dissociative drugs.
Anticholinergic substances. These block the signal that keeps the pupil small. Examples include diphenhydramine (Benadryl) and other antihistamines in overdose, jimsonweed (Datura), scopolamine, and tricyclic antidepressants. Antihistamines are the most common cause of anticholinergic poisoning, which can also cause hot, dry, flushed skin, fever, and confusion. StatPearls: Anticholinergic toxicity; MedlinePlus: Diphenhydramine overdose.
Some antidepressants. The prescribing information for medicines such as sertraline and venlafaxine notes that the pupil dilation seen with many antidepressants can trigger an attack of angle-closure glaucoma in people with narrow eye angles. DailyMed: Zoloft prescribing information. Combining serotonin-affecting drugs can cause serotonin syndrome, a potentially life-threatening reaction that can include dilated pupils, agitation, fever, and muscle twitching. MedlinePlus: Serotonin syndrome.
Dissociatives. Ketamine, dextromethorphan (DXM), and PCP more typically cause jerky eye movements than large pupils, although dilation can occur, especially in an overdose. StatPearls: Dextromethorphan toxicity.
Common medicines that can enlarge the pupils
The American Academy of Ophthalmology lists several everyday medicines that can dilate pupils. AAO: Concerned about dilated pupils?
- Antihistamines and some decongestants
- Some antidepressants, including tricyclics, SSRIs, and SNRIs
- ADHD stimulants such as amphetamine and methylphenidate, whose labels list dilated pupils as a possible effect
- The scopolamine patch for motion sickness, especially if the medicine gets into the eye
- Dilating eye drops used during eye exams, which usually wear off in 4 to 8 hours but can last up to a day
- Medicine from an asthma inhaler that gets into the eye
Do not stop or change a prescribed medicine because of a pupil change. Ask the prescriber or pharmacist first.
Do opioids dilate your pupils?
No. Opioids such as heroin, fentanyl, oxycodone, and morphine usually cause small, "pinpoint" pupils. Pinpoint pupils, slowed breathing, and decreased consciousness are classic signs of an opioid overdose. StatPearls: Opioid toxicity.
Dilated pupils are instead a sign of opioid withdrawal. Clinicians who rate withdrawal symptoms score pupil size as one item on the Clinical Opiate Withdrawal Scale. NIDA: Clinical Opiate Withdrawal Scale. Mixing drugs can also confuse the picture: an opioid and a stimulant taken together can leave the pupils small, large, or normal.
If someone has pinpoint pupils, is breathing slowly, and cannot be woken, call 911 and give naloxone if you have it. MedlinePlus: Opioid overdose.
Does alcohol make your pupils big?
Not usually. In alcohol intoxication, pupil responses are usually preserved, and drug-recognition guidance from the National Highway Traffic Safety Administration describes pupil size as normal with alcohol, although the pupils may react to light more slowly. StatPearls: Ethanol toxicity; NHTSA: Drugs and human performance fact sheets.
Very large pupils in someone who has been drinking point to something else, such as another substance, a medicine, or dim lighting. If a person who has been drinking is confused, very drowsy, breathing poorly, or cannot be woken, treat it as an emergency.
Does weed make your pupils big?
Not reliably. Studies disagree on whether cannabis changes resting pupil size: some find slightly larger pupils, others slightly smaller or no consistent change. The more consistent finding is a slower pupil response to light. Clinical Toxicology: Pupillary dynamics and cannabis inhalation; BMC Ophthalmology: Intravenous THC and pupil size. The best-known eye sign of cannabis use is red, bloodshot eyes rather than large pupils. StatPearls: Cannabis overview.
Can you shrink your pupils after taking drugs?
There is no safe or reliable home method to make drug-dilated pupils smaller. The effect fades as the drug wears off. Do not take another substance or use eye drops to try to change pupil size, which can add new risks. Sunglasses can help with light sensitivity in the meantime.
What matters more than pupil size is how the person is doing overall. If dilated pupils come with any of the warning signs below, get help right away.
When to get medical help
Call 911 if someone with dilated pupils:
- Has a seizure, collapses, or cannot be woken
- Has trouble breathing
- Is severely confused, agitated, or hallucinating
- Has a very high body temperature, hot and dry or heavily sweating skin, or a racing heart
For other questions about a possible poisoning or overdose, call Poison Help at 1-800-222-1222. It is free, confidential, and available 24 hours a day. Poison Control.
Get immediate medical care if the pupils become unequal after a head or eye injury, or if unequal pupils come with vision changes, a drooping eyelid, eye pain, headache, fever, nausea, or a stiff neck. A painful red eye with a dilated pupil and blurred vision can signal angle-closure glaucoma, which is also an emergency. MedlinePlus: Anisocoria.
Contact a doctor for a sudden change in pupil size or pupils that frequently stay dilated without a clear reason. About 1 in 5 people have pupils that are naturally slightly different sizes, which is usually harmless.
Other causes of large pupils
- Dim light, which naturally widens the pupils
- Strong emotion, stress, or excitement
- Naturally large pupils. Normal size ranges from about 2 to 8 millimeters
- Dilating drops from an eye exam
- Eye injuries and certain nerve or brain conditions, which usually affect one pupil more than the other
AAO: Why are my pupils naturally large?
If you are worried about someone's drug use
Pupils are one clue, not proof. NIDA describes the key sign of a drug problem as continued use despite harm to health, school or work, or relationships. Other possible signs include new friends, falling grades or performance, lost interest in activities, changes in sleeping or eating, and more conflict at home. NIDA: Signs of a problem with drugs.
SAMHSA notes that some of these changes can be ordinary growing pains, and that a problem is more likely when several appear together, suddenly, or in an extreme way. SAMHSA: How to tell if your child is drinking. Start with a calm, private conversation about what you have noticed rather than an accusation. Our guides on how to tell if your teenager is using drugs and talking to your teen about treatment can help.
Drug tests can help clarify what is going on, but a positive screen needs lab confirmation, and no test can diagnose addiction. Talk with a healthcare provider about whether testing makes sense. MedlinePlus: Drug testing.
Getting help at Ambrosia
If substance use is affecting you or someone you love, Ambrosia's admissions team can talk through what is happening and the next step. Depending on the assessment, that may include medical detox, addiction treatment, or dual diagnosis care when mental health concerns are also present. For teenagers, ask about The Academy, our adolescent substance use program.